Apple has received a Granted Patent relating to techniques for calibrating an electronic compass that is integrated into an iDevice like the iPhone.

One of the drawbacks of current electronic compass technology, integrated in a portable device such as a smartphone or cellular phone, is that due to being subjected to widespread and variable magnetic interference sources, the compass direction output is in error quite often. This characteristic of the integrated compass may be ameliorated, by using an improved technique that indicates when the environment in which the portable device and/or the magnetic sensor find themselves has changed, such that the calibration process needs to be restarted.

In accordance with an embodiment of the invention, a machine-implemented method for dynamic calibration of a compass in a portable device operates as follows. A magnetic field surrounding the device is monitored during a given time interval, as the portable and its compass function are being used in the normal course by the end user. For example, the magnitude of the magnetic field and the geomagnetic inclination or dip of the geomagnetic field may be monitored during the same time interval. When certain criteria relating to the monitored magnetic field magnitude and geomagnetic inclination angle are met, then this indicates that a new environment has been entered or created around the portable device or the magnetic sensor, such that immediate recalibration is needed.

In another embodiment, in addition to the magnetic field, one or more of position, orientation and movement (POM) of the portable is also monitored during the same interval. Changes in the monitored magnetic field are compared with changes in the monitored POM, to determine when the portable device or magnetic sensor finds itself in a different environment at which time recalibration of the compass is signaled. For example, whenever the change in the monitored magnetic field is large relative to the change in the monitored POM, recalibration of the compass is signaled. As a further example, when the percentage change in the magnetic field is larger than the percentage change in the POM, then recalibration is signaled. This might occur where, for example, the user has been walking for several minutes while carrying the portable and has now gotten into his car; the presence of the car has significantly altered the compass' interference field, but the change in the location of the portable on Earth is by contrast small (in terms of experiencing a change in the geomagnetic field). Other user contexts that can cause an expected change in the monitored magnetic field relative to an expected change in the monitored POM, signifying a change in the environment calling for recalibration, are possible.

Apple credits Patrick Piemonte, Madhu Shrivastav, Puneet Mishra, Robert Mayor, Ronald Huang and Parin as the inventors of granted patent 8,239,153 which was originally filed in Q and published today by the US Patent and Trademark Office.

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